516 
MR. SIBSON ON THE MECHANISM OF RESPIRATION. 
Diagrams. 
H 1 H 2 views looking 
down into the chest; 
a transverse section. 
Diagrams G 1 and G 2 represent side views, and H 1 and H 2 views as if looking 
downwards into the chest, of the rib of an Ass, as in expiration G 1 , H 1 , and Inspiration 
G 2 , II 2 . The downward curve of the upper edge in expiration, G 1 , becomes in G 2 , 
inspiration, a slightly upward curve; G l presents a flat surface, G 2 a thin edge. In 
H 1 , expiration, there is a slight curve on the inner surface ; in H 2 , inspiration, the 
curve is deepened ; and the flat surface of the rib is presented instead of the edge, as 
in H 1 . In fact that curve that looked upward in expiration G 1 looks inward in inspi- 
ration H 2 , and the lateral surface in G 1 , expiration, becomes in H 2 , inspiration, the 
superior surface. 
41 . On inspiration. The oblique internal surf ace of the superior ribs is more nearly 
horizontal. Diagram I 1 I 2 . 
In the Pig, the Sheep, the Calf, and the Ass, the direction of the inner surface of 
the ribs is beautifully adapted to the lungs. The lungs gradually narrow from their 
body upwards to the summit ; the interior of the chest forms as it were a dome at its 
upper part, to contain the upper lobes ; the inner surface of the rib, which on ex- 
piration is nearly vertical, becomes on inspiration much more oblique. The dome 
of the chest is thus increased. 
